The invention relates to creating time-variable digital compositions, and more specifically to controlling the temporal dimension of such compositions.
A composition typically has a sequence of frames, each containing digital data describing, for example, the audio or visual content of the frame. When the composition is played, the frames are output at a composition frame rate. The temporal dimension of a composition is conveyed by the content of the output frames, as well as the rate at which those frames are output.
A composition includes at least one footage item, which also generally contains a sequence of frames. Examples of footage items include video clips, audio clips, and combination video/audio clips. Footage sequences may be individually created and edited, and are integrated to form the output composition. Accordingly, while a footage sequence generally is created at its own frame rate and has a temporal dimension that is controllable independently from that of other footage sequences for the composition, footage sequences are adapted to be output at the composition frame rate.
Thus, the temporal dimension of a footage sequence is controlled by mapping the data of footage frames to create data for the composition frames. Traditionally, the timing of a footage sequence is controlled by duplicating or deleting individual frames. For example, to lengthen the duration of a footage sequence, additional frames are added by duplicating individual existing frames; to shorten the duration of a footage sequence, the number of frames are decreased by deleting individual existing frames. However, editing requiring manual evaluation of individual frames is expensive, and editing without manual evaluation by automated processes can produce frame sequences that do not progress smoothly.